U.S. patent number 4,629,663 [Application Number 06/666,269] was granted by the patent office on 1986-12-16 for removable pressure-sensitive adhesive tape.
This patent grant is currently assigned to Minnesota Mining and Manufacturing Company. Invention is credited to Francis W. Brown, Louis E. Winslow.
United States Patent |
4,629,663 |
Brown , et al. |
December 16, 1986 |
Removable pressure-sensitive adhesive tape
Abstract
The adhesive layer of the novel pressure-sensitive adhesive tape
comprises a polymer of a terminally unsaturated vinyl monomer such
as isooctyl acrylate and an emulsifier monomer such as sodium
styrene sulfonate. Preferably, the adhesive layer also contains a
small amount of a noncationic external emulsifier such as sodium
dodecylbenzene sulfonate. Although the tape has excellent adhesive
properties, it is removable from a variety of surfaces after one
hour at 120.degree. C. and so is useful for purposes such as
automotive masking tape.
Inventors: |
Brown; Francis W. (West St.
Paul, MN), Winslow; Louis E. (Stillwater, MN) |
Assignee: |
Minnesota Mining and Manufacturing
Company (St. Paul, MN)
|
Family
ID: |
24673513 |
Appl.
No.: |
06/666,269 |
Filed: |
October 29, 1984 |
Current U.S.
Class: |
428/343; 526/304;
524/156; 428/355AC; 428/355CN |
Current CPC
Class: |
C09J
133/08 (20130101); C09J 7/385 (20180101); Y10T
428/2887 (20150115); Y10T 428/2891 (20150115); Y10T
428/28 (20150115); C09J 2301/302 (20200801) |
Current International
Class: |
C09J
133/08 (20060101); C09J 7/02 (20060101); C09J
133/06 (20060101); C09J 007/02 () |
Field of
Search: |
;428/343,355,474,336
;524/66,156,814 ;560/193 ;526/304 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Herbert; Thomas J.
Attorney, Agent or Firm: Sell; Donald M. Smith; James A.
Brink; Richard E.
Claims
We claim:
1. Pressure-sensitive adhesive tape comprising a self-substaining
backing sheet carrying a layer of pressure-sensitive adhesive
comprising a copolymer of monomers comprising
(a) from 95 to 99.8 parts by weight of at least one terminally
unsaturated vinyl monomer, 60 to 100 weight percent of said monomer
being selected from the class of nontertiary alkyl acrylates
wherein each alkyl group has at least half of its carbon atoms in a
single chain and the average length of the alkyl chain is at least
4 and not more than 12, and
(b) from 0.2 to 5 parts by weight of at least one vinyl-unsaturated
homopolymerizable emulsifier monomer which is a surfactant having
both a hydrophobic and a hydrophilic moiety, contains at least 5
but no more than 40 carbon atoms, and is water-dispersible, the
total parts by weight (a) plus (b) being 100, wherein the
improvement comprises:
the emulsifer monomer is a monovalent salt of a styrene sulfonate
and wherein the adhesive layer contains up to 1.5% external
emulsifier by weight,
whereby the tape not only has an adhesive value of at least about
40 N/dm and a cohesive value of at least 100 minutes but also can
be cleanly removed from a melamine test surface after one hour at
150? C.
2. Pressure-sensitive adhesive tape as defined in claim 1 wherein
said monomers are free from zwitterion monomer.
3. Pressure-sensitive adhesive tape as defined in claim 1 wherein
the monovalent salt is sodium styrene sufonate.
4. Pressure-sensitive adhesive tape as defined in claim 1 wherein
said vinyl monomer includes an N-substituted acrylamide.
5. Pressure-sensitive adhesive tape as defined in claim 1 wherein
the amount of the emulsifier monomer is from 0.5 to 2 weight
percent.
6. The adhesive of a pressure-sensitive adhesive tape as defined in
claim 1.
Description
FIELD OF THE INVENTION
The invention concerns pressure-sensitive adhesive tapes which
usually are slit to narrow widths and then wound upon themselves
for storage and shipment. Such tapes are originally produced in
wide widths, and the term "tape" encompasses such wide widths. The
invention specifically concerns removable pressure-sensitive
adhesive tapes such as masking tapes, weatherstripping tapes, label
tapes, and protective plating tapes.
BACKGROUND ART
Over a period of many years, the manufacture of pressure-sensitive
adhesive tapes has been shifting from organic solvent systems to
aqueous latices in order to reduce air pollution and fire hazard
and also to eliminate the rising expense of organic solvents.
Surfactants, wetting agents, or emulsifying agents are commonly
used to protect the aqueous latex from coagulation, but as is
pointed out in U.S. Pat. No. 3,551,479 (Emmons), "migration of the
emulsifying agent to the surface of the film has a deleterious
effect upon several properties such as adhesion . . . " (col. 2,
lines 3-5). While the Emmons patent does not mention
pressure-sensitive adhesives it is of interest for its suggestion
of "using an emulsifying agent that is bound to the polymer . . . "
(col. 1, lines 46-47).
U.S. Pat. No. 3,617,368 (Gibbs) concerns heat-sealable barrier
coats made from an aqueous latex including an emulsifying agent
that is bound to the polymer, called a "copolymerizable ionic
material" (col. 3, line 3). The Gibbs patent suggests using "very
small amounts of conventional wetting agents . . . to further aid
in the attainment of particles of desired size" (col. 3, lines
48-55).
U.S. Pat. No. 3,770,708 (Knoepfel et al.) discloses
pressure-sensitive adhesive tape, the adhesive layer of which is a
copolymer of vinyl monomers such as a non-tertiary alkyl acrylate
and zwitterionic monomer which in part serves as an emulsifying
agent that is bound to the polymer. Such emulsifying agents are
hereinafter referred to as "emulsifier monomers". All of the
Knoepfel working examples also employ conventional emulsifying
agents which do not become bound to the polymer and are hereinafter
referred to as "external emulsifiers". The pressure-sensitive
adhesive tape of the Knoepfel patent is characterized by
"outstanding shear strength combined with excellent tack and peel
strength without requiring cure of the adhesive" (col. 2, lines
12-16).
The pressure-sensitive adhesive tape of U.S. Pat. No. 3,922,464
(Silver et al.) is similar to that of the Knoepfel patent except in
these respects: (1) it is removable, (2) from 0.2 to 5% by weight
of at least one vinyl-unsaturated, homopolymerizable emulsifier
monomer is copolymerized with the Knoepfel monomers, and (3) the
zwitterionic monomer can be omitted. In regard to the third
difference, the Silver patent states: "It is often desirable to
incorporate zwitterion monomers into pressure-sensitive adhesives
used in preparing tapes of the present invention. Inclusion of,
e.g., 3-5% (by weight) or more of such monomers greatly improves
the cohesive and shear properties of the adhesive, and even smaller
amounts have beneficial effects" (Col. 4, lines 52-57). Of the
Silver examples, only the tape of Example 2 omits the zwitterion
emulsifier monomers. Recent tests of that tape show submarginal
adhesion and cohesion for many uses.
Most of the zwitterion emulsifier monomers used in the Silver
examples are not currently commercially available and tend to be
expensive to make. At only the 2% weight level used in most of
Silver examples, a zwitterion emulsifier monomer might raise the
price of the tape above what potential users would be willing to
pay.
The Silver adhesives also preferably employ "small amounts of
external emulsifier, especially where short chain emulsifier
monomers are used. Such emulsifiers, which are commonly employed in
the preparation of many copolymer latices, assist in initial
suspension of the monomeric reactants and tend to result in a more
homogeneous appearing emulsion than when they are omitted." (Col.
8, lines 39-55).
U.S. Pat. Nos. 3,931,087 and 4,012,560 (Baatz et al.) concern
pressure-sensitive adhesive tape based on an interpolymer of a
specific sulfonic acid as an emulsifier monomer, an alkyl acrylate
or methacrylate such as 2-ethylhexyl acrylate, and an optional
third monomer such as vinyl acetate. An external emulsifier is
necessary to control the colloidal particle size and to prevent
instability and coagulation of the emulsion (paragraph bridging
cols. 2 and 3 of both Baatz patents).
Members of another class of emulsifier monomers, i.e., sodium
and/or potassium-p-styrene sulfonate, have been copolymerized with
various alkyl acrylates, dienes, styrene, and fluorinated vinyl
monomers to produce polymers which are said to have both improved
heat resistance and tensile strength according to "Polymer
Preprints", Vol. 24 (2), August 1983, pages 37-38, a publication of
Division of Polymer Chemistry, Inc., American Chemical Society.
Specifically reported are tests on copolymers of n-butyl acrylate
and sodium and potassium salts of styrene sulfonate. No mention is
made as to their utility.
U.S. Pat. No. 3,316,200 (Hatala) concerns aqueous paint vehicles
and paints based on copolymers of terminally unsaturated vinyl
monomer, preferably an acrylic polymer, and an emulsifier monomer
which is there called an ionogenic unit. Among a large number of
listed ionogenic units are sodium and potassium styrene
sulfonate.
U.S. Pat. No. 4,387,172 (Agarwal et al.) describes emulsion type
adhesive compositions such as may be obtained by copolymerizing a
conjugated diene such as isoprene with a sulfonate containing
monomer such as sodium styrene sulfonate. To the resultant latex is
added a tackifier resin, and the emulsion is then doctor-bladed
onto a substrate and dried to form a tacky adhesive film.
DISCLOSURE OF INVENTION
The invention provides a pressure-sensitive adhesive tape
comprising a self-sustaining backing sheet carrying a layer of
pressure-sensitive adhesive which can be made from materials that
are currently commercially available, has excellent adhesive and
cohesive strengths, and yet like tapes of the Silver patent can be
cleanly removed from a variety of surfaces after one hour at
120.degree. C. Approximately like adhesives of the Silver patent,
that of the present invention is a copolymer of monomers consisting
essentially of
(a) from 95 to 99.8 parts by weight of at least one terminally
unsaturated vinyl monomer, 60 to 100 weight percent of said vinyl
monomer being selected from the class of nontertiary alkyl
acrylates wherein each alkyl group has at least half of its carbon
atoms in a single chain and the average length of the alkyl chain
is at least 4 and not more than 12, and
(b) from 0.2 to 5 parts by weight of at least one
vinyl-unsaturated, homopolymerizable emulsifier monomer which is a
surfactant having both a hydrophobic and a hydrophilic moiety,
contains at least 5 but not more than 40 carbon atoms, and is
water-dispersible,
the total parts by weight of (a) plus (b) being 100, and said
adhesive layer preferably contains a small amount of an external
emulsifier.
The adhesive of the novel tape differs from that of the Silver
patent in that the emulsifier monomer comprises a monovalent salt
of a styrene sulfonate. As compared to emulsifier monomers named in
the Silver patent, a monovalent salt of a styrene sulfonate more
reliably produces substantially coagulum-free latices, both the
latices and polymers produced therefrom tend to have greater
hydrolytic stability, and latices of higher solids can be obtained
which are easier to coat. By substantially coagulum-free is meant a
latex which neither hangs up on a stirrer nor prematurely plugs up
a filter. In the present invention, a substantially coagulum-free
latex can be obtained without external emulsifier, although at
least 0.05 weight percent of external emulsifier would be preferred
in commercial production to provide a margin of safety. Preferably
the external emulsifier is noncationic and does not exceed 1.5% of
the adhesive layer.
Unlike the adhesives of all but one of the Silver patent examples,
zwitterion monomer is not needed in tapes of the invention to
provide good adhesion and cohesion.
Preferred tapes of the invention have an Adhesive Value (as defined
below) of at least 40 N/dm, and a Cohesive Value (as defined below)
of at least 100 minutes. Even at the significantly higher Adhesive
and Cohesive Values exhibited by preferred tapes of the invention,
such tapes can be cleanly removed from many substrates after one
hour at 120.degree. C. Most of those preferred tapes of the
invention can be cleanly removed from the melamine resin test
surface used in the Silver patent after one hour at 150.degree. C.,
as can many of Silver's tapes. By possessing both clean
removability and high Adhesive and Cohesive values, tapes of the
invention are particularly useful as automotive masking tapes.
Preferably from 0.5 to 2 weight percent of a monovalent salt of a
styrene sulfonate is used in making the copolymer of the adhesive
of the tape of the invention in order to attain desirably high
Cohesive Value. To employ above about 5 weight percent of a
monovalent salt may make it difficult to maintain desirable
Adhesive Values.
Tapes of the invention can be made with terminally unsaturated
vinyl monomers as disclosed in col. 3, line 28 through col. 4, line
2 of the Silver patent. Those used in the examples below are listed
in Table A together with abbreviations used in Table B.
TABLE A ______________________________________ Abbreviations
______________________________________ Acrylate Monomers isooctyl
acrylate IOA isononyl acrylate INA Modifying Comonomers
N--tert-octylacrylamide OACM N--tert-butylacrylamide TBAM
N--tert-amylacrylamide TAAM N--isopropylacrylamide IPAM isobutyl
acrylate IBA ethyl acrylate EA
______________________________________
N-tert-octylacrylamide has the formula CH.sub.2
.dbd.CHCONHC(CH.sub.3).sub.2 CH.sub.2 C(CH.sub.3).sub.3.
Latices of this invention have been made (1) by a single
monomer-charge process, (2) by incremental or continuous monomer
feed processes, and (3) by seed polymerization. A seed latex may
have a composition different from that of the final latex. For
example, the seed latex may omit the emulsifier monomer. Both
persulfate and persulfate-redox initiator systems have been
used.
For uses requiring double-coated tape, a pressure-sensitive
adhesive of the present invention may provide one or both layers.
Such a double-coated tape has been made for a window-insulator kit
to cover windows with sheets of heat-shrinkable, biaxially oriented
polyethylene film. The backing of the tape was biaxially oriented
poly(ethylene terephthalate) film having a thickness of 25
micrometers. The releasable pressure-sensitive adhesive of the
invention covered the face of the tape to be adhered to the window
frame, while the other face was covered by a pressure-sensitive
adhesive having excellent specific adhesion to polyethylene,
namely, a tackified styrene-diene block copolymer. A
window-insulator kit including such a double-coated tape also is
useful for temporarily covering boats and automobiles to protect
them from the elements.
Testing
Before carrying out the tests described below, the tape should be
held at 22.degree. C. and 50% relative humidity for at least 24
hours and preferably more than 48 hours.
Adhesive Value
A strip of tape is adhered by its adhesive to a glass plate under
the weight of one pass of a 2-kg hard rubber roller. The adhesive
value is measured by attaching the free end of the tape to a scale
and moving the glass plate away from the scale at a rate of about
3.8 centimeters per second while peeling the tape at an angle of
180.degree..
Cohesive Value
A strip of tape is adhered by its adhesive to a stainless steel
plate under the weight of two passes of a 2-kg hard rubber roller
with a free end of the tape extending beyond the plate and the
adhesive contact area being 1/2 inch by 1/2 inch (1.27 cm by 1.27
cm . The plate is then positioned 2.degree. from the vertical to
prevent peeling, and a one-kg mass is suspended from the free end.
The time at which the mass falls is the Cohesive value. The test is
discontinued if the tape has not failed after 1000 minutes. Usually
two specimens are tested and the results averaged.
Removability Test
This is the test described in U.S. Pat. No. 3,922,464 in column 7,
lines 29-68. As there reported, removability is tested from glass
microscope slides which have been dipped in catalyzed
hexamethoxymethyl melamine and then cured.
EXAMPLE 1
A split-resin flask of 2000 ml capacity was fitted with a variable
speed agitator, condenser, purging tube for introducing nitrogen,
and a recording controller. The following materials were added to
the flask while purging the flask with nitrogen:
______________________________________ grams
______________________________________ Deionized water 479.6 Sodium
bicarbonate 0.48 Sodium dodecyl benzene sulfonate 1.18 Sodium
styrene sulfonate 3.92 Isooctyl acrylate 341.0
N--tert-octylacrylamide 47.0
______________________________________
The solid N-tert-octylacrylamide was dissolved in the isooctyl
acrylate before adding to the flask. The nitrogen purge was
continued until the end of the run. The flask and its contents were
heated to 40.degree. C., at which temperature a first initiator
charge of 0.24 g of potassium persulfate and 0.08 g of sodium
meta-bisulfite was added.
A change in color of the emulsion indicated the start of
polymerization. The temperature was held near 40.degree. C. by
cooling and heating during the remaining period of reaction. 1.6 ml
of a 5% aqueous solution of sodium meta-bisulfite was added four
hours after the first initiator charge, and 2.4 ml of a 5% aqueous
solution of sodium meta-bisulfite and 2.4 ml of a 5% aqueous
solution of potassium persulfate were added 7 hours after the first
initiator charge. The emulsion was heated another 71/2 hours to
complete polymerization. The resulting latex had no coagulum.
Solids--44.4%
pH--8.0
viscosity--51 cps, Brookfield #1 spindle, 30 rpm.
The latex was coated onto 40-micrometer biaxially oriented
poly(ethylene terephthalate) polyester film and dried to a
thickness of about 28 micrometers. The resulting pressure-sensitive
adhesive tape was tested for
Adhesive Value: 44 N/dm
Cohesive Value: >1000 min.
EXAMPLE 2
The procedure of Example 1 was repeated except as here indicated.
One hour after adding the first initiator charge, the temperature
was raised to 65.degree. C. over a 45-minute period to speed up the
reaction. 2.4 ml of a 5% aqueous solution of sodium meta-bisulfite
and 2.4 ml of a 5% aqueous solution of potassium persulfate were
added three hours after the first initiator charge while the
temperature was held at 65.degree. C. One hour later the emulsion
was cooled. The resulting latex was free of coagulum.
Solids--44.9%
pH--7.7
Viscosity--84 cps.
The latex was coated onto polyester film as in Example 1 to provide
a pressure-sensitive adhesive tape which was tested for
Adhesive Value: 45 N/dm
Cohesive Value: >1000 min.
EXAMPLE 3
The procedure of Example 1 was repeated except that there was only
one initiator charge of 0.8 g potassium persulfate and 0.25 g
sodium meta-bisulfite after which the emulsion was held near
40.degree. C. for 41/2 hours and then cooled to provide a
coagulum-free latex.
Solids--45.4%
pH--8.3
Viscosity--63 cps.
The latex was coated onto polyester film as in Example 1 to provide
a pressure-sensitive adhesive tape which was tested for
Adhesive Value: 46 N/dm
Cohesive Value: >1000 min.
EXAMPLE 4
To a 5000 ml split-resin flask equipped as in Example 1 were added
the following:
______________________________________ grams
______________________________________ Deionized water 1606.0
Sodium bicarbonate 2.4 Sodium styrene sulfonate 20.0 Isooctyl
acrylate 1706.8 1% Solution of tertiary dodecyl mercaptan 33.2 in
isooctyl acrylate N--tert-octylacrylamide 240.0 Sodium dodecyl
benzene sulfonate 6.0 ______________________________________
The flask and its contents were purged with nitrogen while stirring
and heating to 40.degree. C., and a first initiator charge of 1.2 g
potassium persulfate and 0.4 g sodium meta-bisulfite was added.
Polymerization started in about 1/2 hour. The temperature was held
at 40.degree. C. by cooling and heating as required during the
polymerization. 8 ml of a 5% aqueous solution of sodium
meta-bisulfite was added 5 hours after the first initiator charge,
and 12 ml of a 5% aqueous solution of sodium meta-bisulfite and 12
ml of a 5% aqueous solution of potassium persulfate were added 7
hours after the first initiator charge. The emulsion was heated
another 9 hours to complete the polymerization. The resulting latex
had no coagulum.
Solids--54.8%
pH--8.77
Viscosity--1348 cps, Brookfield #3 spindle, 30 rpm.
The latex was coated onto polyester film as in Example 1 and dried
to a thickness of 34 micrometers. The resulting pressure-sensitive
adhesive tape was tested for
Adhesive Value: 58 N/dm
Cohesive Value: >1000 min.
As compared to the tapes of Examples 1, 2, and 3, the improvement
in Adhesive Value is attributed to the small amount of tertiary
dodecyl mercaptan used in the polymerization process.
EXAMPLE 5
Example 4 was repeated except that the tertiary dodecyl mercaptan
was omitted.
Adhesive Value: 47 N/dm
Cohesive Value: >1000 min.
EXAMPLE 6
The following materials were added to a 2000 ml split-resin flask
which was equiped as described in Example 1.
______________________________________ grams
______________________________________ Deionized water 400.0 Sodium
dodecyl benzene sulfonate 4.0 Sodium styrene sulfonate 4.0 Isooctyl
acrylate 316.0 N--Isopropylacrylamide 20.0 Ethyl acryate 60.0
Tertiary dodecyl mercaptan 0.1
______________________________________
The flask and its contents were purged with nitrogen while stirring
and heating to 50.degree. C. At 50.degree. C. was added 1.04 g of a
solution of 0.22 g of ferrous sulfate heptahydrate in 100 g
deionized water, 0.48 g potassium persulfate and 0.24 g sodium
meta-bisulfite. After about 45 minutes, polymerization started and
the temperature rose to 70.degree. C. over a 30-minute period.
After one hour at 70.degree. C., the flask was cooled. The
resulting latex had no coagulum.
Solids--49.3%
pH--5.25
viscosity--15,300 cps
The latex was coated onto polyester film as in Example 1 to provide
a pressure-sensitive tape which was tested for
Adhesive value: 39 N/dm
Cohesive value: >1000
EXAMPLES 7-25
A number of other emulsions were prepared by procedures used in
earlier examples and converted into tapes as in Example 1. The
results reported in Table B include gel fractions in
tetrahydrofuran ("% Gel") of the adhesive layers. Also reported at
the end of Table B as Comparative Example I is a tape made
following Example 2 of U.S. Pat. No. 3,922,464, and as Comparative
Example II, a tape similar to that of Example 12 except for
omission of the monovalent salt of styrene sulfonate.
While the latex used in making the tape of Example 9 in the
laboratory was substantially coagulum-free, its coagulum content
was such that it is doubtful that it could be consistently
manufactured on a commercial scale. Examples 10-12 demonstrated
that increased, but still small, amounts of the external emulsifier
should eliminate this problem.
Removability Testing
Many of the tapes of Examples 1-25 were subjected to the
aforementioned Removability Test. All tapes that were tested were
cleanly removable, as was the tape of Comparative Example I.
TABLE B
__________________________________________________________________________
Adhesive Cohesive Monomers External Emulsifiers Value Value % Ratio
Level (N/dm) (min.) Gel
__________________________________________________________________________
Example 1 IOA:OACM:NaSS 87:12:1 A 0.3 44 >1000 86 2
IOA:OACM:NaSS 87:12:1 A 0.3 45 >1000 83 3 IOA:OACM:NaSS 87:12:1
A 0.3 46 >1000 87 4 IOA:OACM:NaSS 87:12:1 A O.3 58 >1000 NT 5
IOA:OACM:NaSS 87:12:1 A 0.3 47 >1000 NT 6 IOA:EA:IPAM:NaSS
79:15:5:1 A 1.0 39 >1000 NT 7 IOA:OACM:NaSS 87:12:1 None None 41
>1000 NT 8 IOA:OACM:NaSS 87:12:1 A 0.003 41 >1000 NT 9
IOA:OACM:NaSS 87:12:1 A 0.01 42 >1000 NT 10 IOA:OACM:NaSS
87:12:1 A 0.05 45 >1000 NT 11 IOA:OACM:NaSS 87:12:1 A 0.15 47
>1000 NT 12 IOA:OACM:NaSS 87:12:1 A 1.0 48 >1000 82 13
IOA:IBA:NaSS 86:13:1 A 0.3 37 804 87 14 IOA:OACM:NaSS 87:12:1 B 0.3
37 >1000 85 15 IOA:OACM:NaSS 87:12:1 C 0.3 50 >1000 84 16
IOA:OACM:NaSS 87:12:1 D 0.3 46 >1000 82 17 IOA:OACM:NaSS 87:12:1
E 0.3 45 >1000 84 18 IOA:OACM:NaSS 87:12:1 F 0.3 44 >1000 77
19 IOA:NaSS 98.5:1.5 A 0.3 40 >1000 NT 20 IOA:NaSS 99.25:0.75 A
0.3 38 >1000 NT 21 IOA:OACM:NaSS 79.0:19.5:1.5 A 0.3 53 >1000
NT 22 IOA:TBAM:NaSS 91:8:1 A 1.0 51 >1000 NT 23 IOA:EA:TBAM:NaSS
78.5:15:5:1.5 A 1.0 47 >1000 NT 24 IOA:TAAM:NaSS 90.9:8.0:1.1 A
0.3 45 >1000 NT 25 INA:OACM:NaSS 87:12:1 A 0.3 44 >1000 NT
Comparative IOA:IBA:SEMNa 86:13:1 A 2.0 15 3 86 I Comparative
IOA:OACM 87.5:12.5 A 1.0 21 4 NT II
__________________________________________________________________________
NT = not tested NaSS = sodium styrene sulfonate SEMNa = sodium
(2sulfoethyl)methacrylatea A = sodium dodecyl benzene sulfonate B =
sodium alkylaryl polyethoxy sulfonate C = sodium alkylaryl
polyethoxy sulfate D = sodium lauryl sulfate E = nonyl phenol
ethoxylate (10 moles ethylene oxide) F = sodium N--lauryl
betaiminodipropionate
* * * * *